Actuator device and liquid ejection apparatus

ABSTRACT

An actuator device includes: an actuator including piezoelectric elements arranged in a first direction and first contacts arranged in the first direction; a protector including a first wall opposed to the piezoelectric elements and a second wall coupled to the first wall and joined to a region of the actuator at which the first contacts are disposed; first connection terminals disposed on the first; and first through electrodes formed in the second wall to bring the first contacts and the first connection terminals into conduction with each other. A distance between two of the first through electrodes which respectively correspond to two of the piezoelectric elements which are adjacent to each other in the first direction is greater than a distance in the first direction between the two of the piezoelectric elements which are adjacent to each other in the first direction.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 16/379,960,filed Apr. 10, 2019, which is a continuation of U.S. patent applicationSer. No. 15/471,806, filed Mar. 28, 2017, which further claims priorityfrom Japanese Patent Application No. 2016-190054, which was filed onSep. 28, 2016. The disclosures of the aforementioned applications areherein incorporated by reference in their entirety.

BACKGROUND

The following disclosure relates to an actuator device and a liquidejection apparatus.

There is known a liquid ejection apparatus configured to eject liquidfrom nozzles. This liquid ejection apparatus includes: a passage definer(a passage forming base plate) having pressure chambers communicatingwith the respective nozzles; a piezoelectric actuator includingpiezoelectric elements corresponding to the respective pressurechambers; a protector (a protecting base plate) disposed on thepiezoelectric actuator so as to cover the piezoelectric elements; and adrive circuit disposed on an upper surface of the protector.

In this liquid ejection apparatus, contacts drawn out from therespective piezoelectric elements of the piezoelectric actuator areelectrically connected to the drive circuit via respective throughelectrodes extending through the protector.

Specifically, the contacts drawn out from the respective piezoelectricelements are disposed on a portion of the piezoelectric actuator whichis joined to the protector. Through holes are formed in a wall of theprotector which covers the piezoelectric elements. These through holesare filled with a conductive material to form the through electrodes.The contacts drawn out from the piezoelectric actuator and contactsformed on the upper surface of the protector are respectivelyelectrically connected to each other by the through electrodes. Thecontacts formed on the upper surface of the protector are connected tothe drive circuit by wires formed on the upper surface of the protector.

SUMMARY

Incidentally, a construction in which nozzles and pressure chambers aredisposed at high density has been desired in recent years from theviewpoint of size reduction of a liquid ejection apparatus. Here,reduction in arrangement pitches of the pressure chambers reducesarrangement pitches of piezoelectric elements, resulting in smallerarrangement pitches of through electrodes formed on a protector so as tocorrespond to the respective piezoelectric elements.

Furthermore, size reduction of each of the through electrodes isrequired to arrange the through electrodes at small pitches. That is, ifonly the arrangement pitches of the through electrodes are reducedwithout change in size of each through electrode, a distance betweeneach adjacent two of the through electrodes is reduced, resulting inincreased possibility of shorts. In reality, however, there is a limitto reduction in the diameter of each of through holes formed in theprotector, making it difficult to reduce the size of each throughelectrode to a size less than or equal to a particular size.

Accordingly, an aspect of the disclosure relates to a technique forpreventing occurrence of shorts between adjacent through electrodes evenin a construction in which piezoelectric elements are arranged at ashort distance.

In one aspect of the disclosure, an actuator device includes: anactuator including a plurality of piezoelectric elements arranged in afirst direction and a plurality of first contacts respectively drawnfrom the plurality of piezoelectric elements and arranged in the firstdirection; a protector including (i) a first wall opposed to theplurality of piezoelectric elements and (ii) a second wall coupled tothe first wall, the second wall being joined to a region of the actuatorat which the plurality of first contacts are disposed, in a state inwhich the plurality of piezoelectric elements are covered with theprotector; a plurality of first connection terminals disposed on asurface of the first wall of the protector, which surface is located onan opposite side of the first wall from the actuator; and a plurality offirst through electrodes respectively provided in a plurality of firstthrough holes formed in the second wall of the protector, the pluralityof first through electrodes being configured to respectively bring theplurality of first contacts and the plurality of first connectionterminals into conduction with each other. A distance between two of theplurality of first through electrodes which respectively correspond totwo of the plurality of piezoelectric elements which are adjacent toeach other in the first direction is greater than a distance in thefirst direction between the two of the plurality of piezoelectricelements which are adjacent to each other in the first direction.

In another aspect of the disclosure, a liquid ejection apparatusincludes: a passage definer defining therein a plurality of pressurechambers arranged in a first direction and respectively communicatingwith a plurality of nozzles; an actuator including (a) a plurality ofpiezoelectric elements respectively corresponding to the plurality ofpressure chambers and (b) a plurality of first contacts respectivelydrawn from the plurality of piezoelectric elements and arranged in thefirst direction; a protector including (i) a first wall opposed to theplurality of piezoelectric elements and (ii) a second wall coupled tothe first wall, the second wall being joined to a region of the actuatorat which the plurality of first contacts are disposed, in a state inwhich the plurality of piezoelectric elements are covered with theprotector; a plurality of first connection terminals disposed on asurface of the first wall of the protector, which surface is located onan opposite side of the first wall from the actuator; and a plurality offirst through electrodes respectively provided in a plurality of firstthrough holes formed in the second wall of the protector, the pluralityof first through electrodes being configured to respectively bring theplurality of first contacts and the plurality of first connectionterminals into conduction with each other. A distance between two of theplurality of first through electrodes which respectively correspond totwo of the plurality of piezoelectric elements which are adjacent toeach other in the first direction is greater than a distance in thefirst direction between the two of the plurality of piezoelectricelements which are adjacent to each other in the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, advantages, and technical and industrialsignificance of the present disclosure will be better understood byreading the following detailed description of the embodiment, whenconsidered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic plan view of a printer according to oneembodiment;

FIG. 2 is a top view of a head unit;

FIG. 3 is a top view of the head unit, with a driver IC and an FPC beingsimplified;

FIG. 4 is a top view of the head unit, without illustration of aprotector;

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4;

FIGS. 6A and 6B are cross-sectional views of a separated wall of theprotector, wherein

FIG. 6A is a cross-sectional view of a portion of the separated wall atwhich first through electrodes are formed, and FIG. 6B is across-sectional view of a portion of the separated wall at which secondthrough electrodes are formed;

FIG. 7 is a view illustrating a positional relationship amongpiezoelectric elements, driving contacts, and the first throughelectrodes;

FIG. 8 is a view illustrating a positional relationship among thepiezoelectric elements, the driving contacts, and the first throughelectrodes in a comparative example;

FIGS. 9A through 9F are views illustrating a process of producing theprotector;

FIGS. 10G through 10I are views illustrating a process from joining ofthe protector to joining of the driver IC and the FPC;

FIG. 11 is a cross-sectional view of a portion of a protector at whichfirst through electrodes are formed in a modification;

FIG. 12 is a cross-sectional view of a portion of a protector at whichfirst through electrodes are formed in another modification;

FIG. 13 is a top view of a head unit in yet another modification;

FIG. 14 is a top view of a head unit in yet another modification;

FIG. 15 is a cross-sectional view of the head unit in FIG. 14;

FIG. 16 is a cross-sectional view of a head unit in yet anothermodification;

FIG. 17 is a cross-sectional view of a head unit in yet anothermodification;

FIG. 18 is a view illustrating a positional relationship among thepiezoelectric elements, the driving contacts, and the first throughelectrodes in the head unit in FIG. 17;

FIG. 19 is a view illustrating a positional relationship among thepiezoelectric elements, driving contacts, and the first throughelectrodes in yet another modification; and

FIG. 20 is a top view of the head unit in yet another modification.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, there will be described an embodiment by reference to thedrawings. First, there will be explained an overall configuration of anink-jet printer 1 with reference to FIG. 1. The direction in which arecording sheet 100 is conveyed in FIG. 1 is defined as the front andrear direction of the printer 1. The widthwise direction of therecording sheet 100 is defined as the right and left direction of theprinter 1. The direction orthogonal to the front and rear direction andthe right and left direction and perpendicular to the sheet surface ofFIG. 1 is defined as the up and down direction of the printer 1.

Overall Configuration of Printer

As illustrated in FIG. 1, the ink-jet printer 1 includes a platen 2, acarriage 3, an ink-jet head 4, a conveying mechanism 5, and a controller6.

The carriage 3 is mounted on guide rails 10, 11 extending in the rightand left direction (hereinafter may also be referred to as “scanningdirection”). The carriage 3 is joined to a carriage driving motor 15 viaan endless belt 14. The carriage 3 is driven by the motor 15 andreciprocated in the scanning direction over the recording sheet 100conveyed on the platen 2.

The ink-jet head 4 is mounted on the carriage 3 and moved in thescanning direction with the carriage 3. The ink-jet head 4 includes fourhead units 16 arranged in the scanning direction. The four head units 16are respectively connected to ink cartridges 17 held by a holder 7. Theink cartridges 17 respectively contain inks of four colors, namely,black, yellow, cyan, and magenta.

Each of the head units 16 has a multiplicity of nozzles 36 (see FIGS. 4and 5) formed in its lower surface (located on a back-surface-side ofthe sheet of FIG. 1). The inks are supplied from the respective inkcartridges 17 to the respective head units 16, and the head units 16eject the respective inks onto the recording sheet 100 placed on theplaten 2. The construction of the head units 16 will be described laterin detail.

The conveying mechanism 5 includes two conveying rollers 18, 19configured to convey the recording sheet 100 on the platen 2 in thefront direction (hereinafter may also be referred to as “conveyingdirection”). The controller 6 controls devices including the ink-jethead 4 and the carriage driving motor 15 to print an image on therecording sheet 100 based on a print instruction received from anexternal device such as a personal computer (PC).

Detailed Configuration of Ink-Jet Head

There will be next described the construction of the head units 16 ofthe ink-jet head 4 in detail. It is noted that the four head units 16have the same construction, and the following description will beprovided for one of the four head units 16 for simplicity.

As illustrated in FIGS. 2-5, the head unit 16 includes a first passagedefiner 21, a second passage definer 22, a nozzle plate 23, and anactuator device 25. The actuator device 25 includes a piezoelectricactuator 24. In the present embodiment, the actuator device 25 does notindicate only the piezoelectric actuator 24 but includes not only thepiezoelectric actuator 24 but also a protector 26, a driver integratedcircuit (IC) 37 joined to the protector 26, and a flexible printedcircuit (FPC) 27 as one example of a wiring member.

First Passage Definer, Second Passage Definer, and Nozzle Plate

First, the first passage definer 21, the second passage definer 22, andthe nozzle plate 23 will be described. Each of these components is abase plate formed of silicon single crystal. The first passage definer21, the second passage definer 22, and the nozzle plate 23 are stackedon each other in the up and down direction in this order from above.

The first passage definer 21 has a multiplicity of pressure chambers 28arranged on a horizontal plane. Each of the pressure chambers 28 has arectangular shape elongated in the scanning direction. The pressurechambers 28 are arranged in the conveying direction so as to form twopressure chamber rows arranged in the scanning direction. Positions ofthe pressure chambers 28 in the conveying direction are differentbetween the two pressure chamber rows. More specifically, in the casewhere the arrangement pitch of the pressure chambers 28 in each of thepressure chamber row is defined as P0, the positions of the pressurechambers 28 in the conveying direction are displaced by a distance ofP0/2 between the right and left pressure chamber rows.

As illustrated in FIG. 5, a vibration layer 40 of the piezoelectricactuator 24, which will be described below, is formed on an uppersurface of the first passage definer 21 so as to cover the pressurechambers 28. The vibration layer 40 is formed by oxidation or nitridingof a surface of a substrate formed of silicon, for example.

As illustrated in FIGS. 2-4, the second passage definer 22 is one sizelarger than the first passage definer 21 in plan view and stuck out fromthe entire perimeter of the first passage definer 21 when viewed fromabove. As illustrated in FIGS. 4 and 5, two manifolds 30 correspondingto the respective two pressure chamber rows are respectively formed inright and left end portions of the second passage definer 22 which arestuck out from the first passage definer 21. The ink is supplied fromthe ink cartridge 17 (see FIG. 1) to the two manifolds 30. That is, thetwo manifolds 30 receive the ink of the same color. Each of themanifolds 30 communicates with the pressure chambers 28 forming acorresponding one of the pressure chamber rows.

The nozzle plate 23 has the nozzles 36 corresponding to the respectivepressure chambers 28. The nozzles 36 communicate with the respectivepressure chambers 28 formed in the first passage definer 21. The nozzles36 are arranged in two rows corresponding to the respective two rows ofthe pressure chambers 28. The positions of the nozzles 36 in theconveying direction are displaced by the distance of P0/2 between thetwo nozzle rows.

Piezoelectric Actuator Device

The actuator device 25 is disposed on the upper surface of the firstpassage definer 21. The actuator device 25 includes the piezoelectricactuator 24, the protector 26, the driver IC 37, and the FPC 27. Thepiezoelectric actuator 24 includes piezoelectric elements 41.

Piezoelectric Actuator

The piezoelectric actuator 24 is disposed on the entire upper surface ofthe first passage definer 21. As illustrated in FIGS. 4 and 5, thepiezoelectric actuator 24 includes the vibration layer 40 and thepiezoelectric elements 41 arranged on the vibration layer 40.

As described above, the vibration layer 40 is formed on the uppersurface of the first passage definer 21 so as to cover the pressurechambers 28. The vibration layer 40 has a thickness of 1.0 μm to 1.5 μm,for example. The piezoelectric elements 41 are disposed on an uppersurface of the vibration layer 40 at positions overlapping therespective pressure chambers 28. In accordance with the arrangement ofthe pressure chambers 28, the piezoelectric elements 41 form twopiezoelectric element rows 47 arranged in the scanning direction. Thepositions of the piezoelectric elements 41 in the front and reardirection are displaced by the distance of P0/2 between the twopiezoelectric element rows 47.

The construction of each of the piezoelectric elements 41 will bedescribed. Each of the piezoelectric elements 41 includes: a lowerelectrode 42 disposed on the vibration layer 40; a piezoelectric layer43 disposed on the lower electrode 42; and an upper electrode 44disposed on the piezoelectric layer 43.

The lower electrodes 42 are disposed on the upper surface of thevibration layer 40 so as to overlap the respective pressure chambers 28.The lower electrodes 42 are individual electrodes separated from eachother so as to respectively corresponding to the piezoelectric elements41. Drive signals are supplied from the driver IC 37 individually to thelower electrodes 42 of the respective piezoelectric elements 41. Asillustrated in FIGS. 4 and 7, one end portion of the lower electrode 42extends inward in the scanning direction so as to be exposed from acorresponding one of piezoelectric members 46. The lower electrodes 42are formed of platinum (Pt), for example. Each of the lower electrodes42 has a thickness of 0.1 for example.

The piezoelectric layers 43 are formed of a piezoelectric material suchas lead zirconate titanate (PZT). Each of the piezoelectric layers 43has a thickness of 1.0 μm to 2.0 for example. In the present embodiment,as illustrated in FIGS. 3-5, the piezoelectric layers 43 are connectedto each other among the piezoelectric elements 41 in the leftpiezoelectric element row 47, and the piezoelectric layers 43 areconnected to each other among the piezoelectric elements 41 in the rightpiezoelectric element row 47. That is, the piezoelectric member 46covering the left pressure chamber row and the piezoelectric member 46covering the right pressure chamber row are disposed on the vibrationlayer 40.

The upper electrodes 44 are disposed on upper surfaces of the respectivepiezoelectric layers 43. The upper electrodes 44 are formed of iridium(Ir), for example. Each of the upper electrodes 44 has a thickness of0.1 μm, for example. The upper electrodes 44 corresponding to therespective pressure chambers 28 are connected to each other on an uppersurface of each of the piezoelectric members 46 so as to form a commonelectrode 49 covering the substantially entire upper surface of thepiezoelectric member 46. It is noted that ground potential is applied tothe upper electrodes 44 (the common electrodes 49) from the FPC 27 whichwill be described below. Subsidiary conductors 50 are provided on therespective common electrodes 49. The thickness of each of the subsidiaryconductors 50 is greater than that of each of the common electrodes 49.The subsidiary conductors 50 are formed of gold (Au), for example.

Driving wires 52 are respectively connected to end portions of therespective lower electrodes 42 which are exposed from the piezoelectricmember 46. Each of the driving wires 52 extends inward in the scanningdirection from the end portion of a corresponding one of the lowerelectrodes 42. The driving wires 52 are made of gold (Au), for example.

The driving wires 52 extend to a region located between the twopiezoelectric element rows 47. Driving contacts 57 are provided on endportions of the respective driving wires 52. The driving contacts 57 ofthe respective driving wires 52 are arranged in the conveying directionin two rows at the region located between the two piezoelectric elementrows 47. More specifically, as illustrated in FIGS. 4 and 7, two contactrows 56 are arranged side by side in the right and left directionbetween the two piezoelectric element rows 47, and these two contactrows 56 include: a contact row 56 constituted by the driving contacts 57drawn out from the left piezoelectric element row 47; and a contact row56 constituted by the driving contacts 57 drawn out from the rightpiezoelectric element row 47. Like the two piezoelectric element rows47, the positions of the driving contacts 57 in the front and reardirection are displaced by the distance of P0/2 between the two contactrows 56.

As illustrated in FIG. 4, the two common electrodes 49 disposed on theupper surfaces of the respective two piezoelectric members 46 areconnected to each other by electrically-conductive portions 50 a of thesubsidiary conductors 50 which extend astride the two piezoelectricmembers 46. Ground contacts 58 are provided on the respectiveelectrically-conductive portions 50 a at positions arranged next to thedriving contacts 57 in the front and rear direction. That is, thedriving contacts 57 and the two ground contacts 58 respectively locatedin front of and at a rear of the driving contacts 57 in the front andrear direction are disposed between the two piezoelectric element rows47.

Protector, Driver IC, and FPC

As illustrated in FIGS. 2-5, the protector 26 is joined to an uppersurface of the piezoelectric actuator 24 with adhesive so as to coverthe piezoelectric elements 41. Conductive adhesive 60 containingconductive particles is used as the adhesive. The material of theprotector 26 is not limited in particular. A silicon base is preferablyemployed for the protector 26.

As illustrated in FIG. 5, the protector 26 includes a top wall 53, twoside walls 54, and a separated wall 55. The top wall 53 is opposed tothe piezoelectric elements 41. The two side walls 54 are respectivelycoupled to opposite end portions of the top wall 53 in the right andleft direction. Each of the two side walls 54 extends in the front andrear direction (in a direction perpendicular to the sheet surface ofFIG. 5). The separated wall 55 is coupled to a central portion of thetop wall 53 in the right and left direction and extends in the front andrear direction between the two side walls 54.

The two side walls 54 of the protector 26 are joined to the uppersurface of the piezoelectric actuator 24 at its regions respectivelylocated on opposite outer sides of the two piezoelectric element rows 47in the right and left direction. The separated wall 55 is joined to theupper surface of the piezoelectric actuator 24 at its region locatedbetween the two piezoelectric element rows 47, i.e., at its region onwhich the contacts 57, 58 are disposed. The interior space of theprotector 26 is partitioned by the separated wall 55 into two spacescontaining the respective right and left piezoelectric element rows 47.In the present embodiment, the width of the separated wall 55 in theright and left direction is greater than that of each of the side walls54 in the right and left direction.

The driver IC 37 is disposed on an upper surface of the top wall 53 atits central portion in the right and left direction which is coupled tothe separated wall 55. The FPC 27 is bonded to the upper surface of thetop wall 53 at its right end portion coupled to the right side wall 54.

The protector 26 plays not only a role in protecting the piezoelectricelements 41 but also a role as a component on which wires for connectingbetween (i) the contacts 57, 58 of the piezoelectric actuator 24 and(ii) the driver IC 37 and the FPC 27 are to be formed. There will beexplained a wiring structure of the protector 26 for connecting between(i) the piezoelectric actuator 24 and (ii) the driver IC 37 and the FPC27.

As illustrated in FIGS. 2 and 3, input terminals 61 arranged in thefront and rear direction are disposed on the upper surface of the topwall 53 at its right end portion coupled to the right side wall 54. Theinput terminals 61 include signal input terminals 62 and ground inputterminals 63. The FPC 27 is bonded to a right end portion of the topwall 53 with conductive adhesive 64, so that the FPC 27 and the inputterminals 61 are electrically connected to each other. An end portion ofthe protector 26 which is located on an opposite side thereof from theFPC 27 is connected to the controller 6 (see FIG. 1) of the printer 1.

A plurality of individual terminals 65, two first ground terminals 67, aplurality of signal terminals 66, and two second ground terminals 70arranged in the front and rear direction are formed on the upper surfaceof the central portion of the top wall 53 of the protector 26 in theright and left direction, which central portion is coupled to theseparated wall 55.

The individual terminals 65 corresponding to the respective drivingcontacts 57 of the piezoelectric actuator 24 are arranged in two rows ina staggered configuration. The two first ground terminals 67respectively corresponding to the two ground contacts 58 of thepiezoelectric actuator 24 are respectively located on opposite sides ofthe individual terminals 65 in the front and rear direction. The signalterminals 66 are arranged in the front and rear direction at a regionlocated to the right of the individual terminals 65. The two secondground terminals 70 are respectively located on opposite sides of theindividual terminals 65 in the front and rear direction.

The driver IC 37 is joined to the upper surface of the central portionof the top wall 53 in the right and left direction with the conductiveadhesive 64, and the individual terminals 65, the signal terminals 66,and the two ground terminals 70 are electrically connected to the driverIC 37.

The signal input terminals 62 connected to the FPC 27 and the signalterminals 66 connected to the driver IC 37 are respectively connected toeach other by signal wires 68 extending in the right and left directionon the upper surface of the top wall 53. The ground input terminals 63are connected to the respective first ground terminals 67 and therespective second ground terminals 70 by respective ground wires 69(wire portions 69 a, 69 b) formed on the upper surface of the top wall53. Specifically, the ground input terminals 63 are connected to therespective first ground terminals 67 by the respective wire portions 69a extending in the right and left direction and in the front and reardirection. The ground input terminals 63 are connected to the respectivesecond ground terminals 70 by the respective wire portions 69 b, each ofwhich is branched off from a portion of a corresponding one of the wireportions 69 a and extends in the right and left direction. It is notedthat the wires and the terminals on the top wall 53, such as the signalwires 68, the ground wires 69, the individual terminals 65, the signalterminals 66, the ground terminals 67, 70, and the input terminals 61,are made of gold (Au), for example.

A plurality of first through electrodes 71 and two second throughelectrodes 72 are formed in the separated wall 55. The first throughelectrodes 71 extend in the up and down direction. The two secondthrough electrodes 72 are disposed on opposite sides of the firstthrough electrodes 71 in the front and rear direction. The first throughelectrodes 71 conduct with the respective driving contacts 57 disposedon the piezoelectric actuator 24 and with the respective individualterminals 65 disposed on the top wall 53 which are located above thedriving contacts 57. The second through electrodes 72 conduct with therespective ground contacts 58 disposed on the piezoelectric actuator 24and with the respective first ground terminals 67 disposed on the topwall 53 which are located above the ground contacts 58.

The controller 6 inputs control signals to the driver IC 37 via the FPC27, the signal input terminals 62 disposed on the protector 26, thesignal wires 68, and the signal terminals 66. The driver IC 37 outputsthe drive signal to each of the piezoelectric elements 41 based on thecontrol signals. The drive signals are applied to the respective lowerelectrodes 42 of the piezoelectric elements 41 via the respectiveindividual terminals 65, the respective first through electrodes 71, andthe respective driving contacts 57 of the piezoelectric actuator 24.

Though not illustrated, ground wires are formed on the FPC 27. Theseground wires are connected to the common electrodes 49 (the upperelectrodes 44) of the piezoelectric actuator 24 via the ground inputterminals 63, the wire portions 69 a, the first ground terminals 67, thesecond through electrodes 72, and the ground contacts 58. As a result,electric potential of the upper electrodes 44 is kept at groundpotential. The ground wires formed on the FPC 27 are also connected tothe driver IC 37 via the ground input terminals 63, the wire portions 69b, and the second ground terminals 70.

As illustrated in FIGS. 2 and 3, the individual terminals 65 disposed onthe top wall 53 correspond to the respective piezoelectric elements 41,and the number of the individual terminals 65 is equal to the number ofthe driving contacts 57. In contrast, the input terminals 61 (62, 63)connected to the FPC 27 are terminals to which signals principally forcontrolling the driver IC 37 are to be supplied, and the number of theinput terminals 61 is less than the number of the individual terminals65. Thus, the arrangement length of the input terminals 61 in the frontand rear direction is less than that of the individual terminals 65 inthe front and rear direction. In addition, in the present embodiment,the width of the FPC 27 in the front and rear direction is less thanthat of the driver IC 37 in the front and rear direction, resulting inreduced size of the FPC 27 and reduced cost. Also, the reduced width ofthe FPC 27 facilitates arrangement of the FPC 27. Details of ThroughElectrodes

There will be next explained the through electrodes 71, 72 formed in theseparated wall 55 of the protector 26. As illustrated in FIGS. 5 and 6A,a plurality of first through holes 73 are formed through the separatedwall 55 in the up and down direction at its central portion in the rightand left direction so as to overlap the respective driving contacts 57.Each of the first through holes 73 is filled with a conductive materialsuch as copper (Cu), and the first through electrodes 71 each extendingin the up and down direction are formed in the respective first throughholes 73.

As illustrated in FIGS. 5 and 6B, two second through holes 74 are formedin the separated wall 55 at its central portion in the right and leftdirection so as to respectively overlap the front and rear groundcontacts 58. Like the first through holes 73, each of the two secondthrough holes 74 is filled with the same conductive material as providedin the first through holes 73, and the two second through electrodes 72each extending in the up and down direction are formed in the respectivesecond through holes 74. In the present embodiment, the diameter of eachof the second through holes 74 is equal to that of each of the firstthrough holes 73. That is, the diameter of each of the second throughelectrodes 72 is equal to that of each of the first through electrodes71.

Since the driving contacts 57 drawn out from the two piezoelectricelement rows 47 are arranged at high density between the twopiezoelectric element rows 47, the area of each of the driving contacts57 is small. As explained later, however, it is difficult to reduce thediameter of each of the first through holes 73 to a size approximatelyequal to that of each of the driving contacts 57 by etching, so thateach of the first through holes 73 has a diameter greater than or equalto a certain diameter. Thus, as illustrated in FIGS. 6A and 7, the areaof a lower end face of each of the first through electrodes 71 isgreater than the area of the driving contact 57 provided on a distal endportion of a corresponding one of the driving wires 52. Morespecifically, the diameter of the lower end face of the first throughelectrode 71 is greater than the width of the driving contact 57 in thefront and rear direction. For the same reason, as illustrated in FIGS. 3and 5, each of the individual terminals 65 disposed on the upper endsurface of the top wall 53 is also smaller than a corresponding one ofthe first through electrodes 71. That is, the area of an upper end faceof the first through electrode 71 is greater than that of the area ofthe individual terminal 65 disposed on the upper surface of the top wall53.

Since a large amount of current flows in the common electrodes 49 whenmany piezoelectric elements 41 are driven at the same time, a resistanceof paths connected to the common electrode 49 needs to be small in orderto prevent a drop in voltage. From this point of view, as illustrated inFIGS. 2, 3, and 6B, the area of each of the ground contacts 58 and thefirst ground terminals 67 is greater than the area of an end face of acorresponding one of the second through electrodes 72.

In addition, insulating layers 75, 76 are respectively formed on a lowersurface of the protector 26 which is joined to the piezoelectricactuator 24 and an upper surface of the protector 26 which is anopposite surface of the protector 26 from the lower surface. Holes 75 aare formed in the lower insulating layer 75 respectively at positionsoverlapping the respective first through holes 73. The area of each ofthe holes 75 a is less than that of the lower end face of acorresponding one of the first through electrodes 71. That is, the hole75 a limits the exposed area of the lower end face of the first throughelectrode 71 (the area of a portion of the lower end face which isjoined to the driving contact 57) to a small area. Holes 76 a arerespectively formed in portions of the upper insulating layer 76 whichoverlap the respective first through holes 73. The area of each of theholes 76 a is less than that of an upper end face of a corresponding oneof the first through electrodes 71. The hole 76 a limits the exposedarea of the upper end face of the first through electrode 71 (the areaof a portion of the upper end face which is joined to the individualterminal 65) to a small area. It is noted that holes 75 b are formed inthe insulating layer 75 at positions respectively overlapping the secondthrough holes 74, and holes 76 b are formed in the insulating layer 76at positions respectively overlapping the second through holes 74. Thearea of each of the holes 75 b, 76 b is substantially equal to the areaof the end face of each of the second through electrodes 72.

The protector 26 is joined to the upper surface of the piezoelectricactuator 24 with the conductive adhesive 60. The conductive adhesive 60(ACF or ACP) is formed by mixing conductive particles into thermosettingresin such as epoxy resin. Each of the contacts 57, 58 of thepiezoelectric actuator 24 and a corresponding one of the throughelectrodes 71, 72 formed in the protector 26 electrically conduct witheach other by the conductive particles contained in the conductiveadhesive 60.

Each of the contacts 57 and the corresponding through electrode 71 areheated and pressed against each other in a state in which the conductiveadhesive 60 is interposed between each of the contacts 57 provided onthe piezoelectric actuator 24 and the corresponding through electrode 71provided on the protector 26. Each of the contacts 58 and thecorresponding through electrode 72 are heated and pressed against eachother in a state in which the conductive adhesive 60 is interposedbetween each of the contacts 58 provided on the piezoelectric actuator24 and the corresponding through electrode 72 provided on the protector26. In these operations, the adhesive 60 is compressed between each ofthe contacts 57, 58 and the corresponding one of the through electrodes71, 72, so that each of the contacts 57, 58 and the corresponding one ofthe through electrodes 71, 72 are electrically connected to each otherby the conductive particles contained in the adhesive 60. At the sametime, the thermosetting resin as the main components of the adhesive 60flows out from between each of the contacts 57, 58 and the correspondingone of the through electrodes 71, 72 to areas around the contacts 57, 58and the through electrodes 71, 72 and is hardened by heat. As a result,the piezoelectric actuator 24 and the protector 26 are mechanicallyjoined to each other. In FIGS. 5-6B, thick hatching indicates portionsof the conductive adhesive 60 between the contacts 57, 58 and therespective through electrodes 71, 72, in particular, portions of theconductive adhesive 60 at which the contacts 57, 58 and the respectivethrough electrodes 71, 72 conduct with each other by the conductiveadhesive 60 to distinguish the portions from mechanically joinedportions therearound.

Incidentally, in particular, from the viewpoint of arrangement of manyfirst through electrodes 71 at high density, the diameter of each of thefirst through holes 73 is preferably small. In reality, however, thereis a limit to reduction of the diameter of each of the first throughholes 73.

This limit will be explained, taking a case where the through holes areformed by etching as one example. In the case where the thickness of acomponent in which holes are to be formed is defined as t, the minimumvalue of the diameter of each hole formed by etching is about t/10. Thatis, the diameter of each through hole is prone to increase with increasein the thickness of the component. Here, the protector 26 is originallyfor protecting the piezoelectric elements 41, and the thickness ofgreater than or equal to a certain thickness is required for achievingthe protecting function. Also, in the case where the thickness of theprotector 26 is small, handling when the protector 26 is joined to thepiezoelectric actuator 24 is difficult. Thus, the thickness of greaterthan or equal to a certain thickness is required for the protector 26also from this viewpoint. In view of the above, in the case where thefirst through holes 73 are formed by etching, the diameter of each ofthe formed first through holes 73 is large in some degree.

The large diameter of each first through hole 73 reduces a distancebetween adjacent two of the first through electrodes 71, resulting inincrease in possibility of occurrence of shorts between the adjacent twofirst through electrodes 71. In particular, in the present embodiment,the protector 26 is joined to the piezoelectric actuator 24 with theconductive adhesive 60, and when the conductive particles contained inthe conductive adhesive 60 flow out to the areas around the contactstogether with the thermosetting resin, a possibility of shorts due tothe conductive particle increases with decrease in the distance betweenthe first through electrodes 71.

To solve this problem, in the present embodiment, the followingconstruction is employed to reduce the distance between the adjacentfirst through electrodes 71 in the front and rear direction. First, asdescribed above, the driving contacts 57 of the piezoelectric actuator24 are arranged in a staggered configuration so as to form the twocontact rows 56. In accordance with the arrangement of the drivingcontacts 57, as illustrated in FIGS. 3 and 7, the first throughelectrodes 71 are also arranged in a staggered configuration so as toform two electrode rows 77 arranged in the right and left direction andeach extending in the front and rear direction. As in the two contactrows 56, the positions of the first through electrodes 71 in the frontand rear direction are displaced by a distance P1 (which is equal toP0/2) between the two electrode rows 77.

In the present embodiment, as illustrated in FIG. 7, a distance P2between two of the first through electrodes 71 which are correspond toadjacent two of the piezoelectric elements 41 in the front and reardirection is greater than a distance P1 between the two piezoelectricelements 41. Specifically, the distance between the first throughelectrodes 71 is the smallest in the case where the first throughelectrodes 71 are arranged in a direction along a straight line Lconnecting between the center of the first through electrode 71 in theleft electrode row 77 and the center of the first through electrode 71in the right electrode row 77. In the present embodiment, the distanceP2 between the two first through electrodes 71 along the straight line Lis greater than the distance P1 (=P0/2) in the front and rear directionbetween the two piezoelectric elements 41 corresponding to therespective two first through electrodes 71.

FIG. 8 illustrates a comparative example of the construction in FIG. 7.In the example in FIG. 8, the driving contacts 57 drawn out from the twopiezoelectric element rows 47 are arranged in a row in the front andrear direction at the intervals P1. In this construction, the distancebetween the closest two first through electrodes 71 is P1. In theconstruction in FIG. 7 in the present embodiment, in contrast, thedistance between the closest two first through electrodes 71 is greaterthan P1. In other words, in the present embodiment, the driving contacts57 provided on the piezoelectric actuator 24 are divided into the rightand left contact rows 56, and the first through electrodes 71 providedon the protector 26 are divided into the right and left electrode rows77, whereby the shortest distance between the adjacent first throughelectrodes 71 is large.

For example, as described above, in the case where the thickness t ofthe protector 26 is 400 the diameter d of each of the first throughholes 73 is 40 μm (=t/10) at the shortest. In the case where thearrangement pitch P0 of the nozzles 36 in each of the nozzle rows is 300dpi (=84 μm), the distance P1 between the two piezoelectric elements 41adjacent to each other in the front and rear direction is P0/2 (=42 μm).In this case, if the first through electrodes 71 are arranged in a rowat the pitches of P1 in the front and rear direction as illustrated inFIG. 8, little space remains between the two first through electrodes 71adjacent to each other in the front and rear direction. As illustratedin FIG. 7, in contrast, in the case where the first through electrodes71 are arranged in the right and left electrode rows 77, the distance P2between the first through electrodes 71 close to each other can beincreased to about 60 μm.

Thus, the distance P2 between the two first through electrodes 71respectively corresponding to the two piezoelectric elements 41 adjacentto each other in the front and rear direction is greater than thedistance P1 between the two piezoelectric elements 41 in the front andrear direction. With this construction, even in the case where thearrangement pitch P0 in the one nozzle rows is considerably small (e.g.,300 dpi), it is possible to prevent shorts between the two first throughelectrodes 71 adjacent to each other.

As illustrated in FIG. 6A, the lower end face of each of the firstthrough electrodes 71 is covered with the insulating layer 75 having thesmall holes 75 a, whereby the area of the lower end face of each of thefirst through electrodes 71 is substantially made smaller. In thisconstruction, the space between the adjacent first through electrodes 71is large at their lower ends joined to the respective driving contacts57, thereby more reliably preventing shorts. The above-describedconstruction is effective in particular in the case where the area ofthe lower end face of each of the first through electrodes 71 is greaterthan the area of the corresponding driving contact 57.

Also, the upper end faces of the respective first through electrodes 71are covered with the insulating layer 76 having the small holes 76 a,whereby the area of each of the upper end faces of the respective firstthrough electrodes 71 is substantially made smaller. As a result, thespace between the adjacent first through electrodes 71 is also large attheir upper ends joined to the driver IC 37, thereby more reliablypreventing shorts.

To reduce the resistance of the paths connected to the common electrodes49, as illustrated in FIG. 3, a plurality of the second throughelectrodes 72 are preferably provided for connection to the commonelectrodes 49. It is noted that it is possible to lower the resistanceof the paths connected to the common electrodes 49 by making thediameter of each of the second through holes 74 greater than that ofeach of the first through holes 73. However, in the case where the firstthrough holes 73 and the second through holes 74 have the same diameteras in the present embodiment, when the first through holes 73 and thesecond through holes 74 are formed by etching, shapes of masks need notbe different from each other, facilitating formation of the holes.

However, it is not preferable to increase the number of the secondthrough electrodes 72 more than needed, because this increase leads tolarger sizes of the piezoelectric actuator 24 and the protector 26. Tosolve this problem, the number of the second through electrodes 72 andthe diameter of each of the second through electrodes 72 may bedetermined based on the following expression, for example.

Here, the number of the second through electrodes 72 and the diameter ofeach of the second through electrodes 72 are determined such that acurrent greater than an allowable current value does not pass throughthe second through electrodes 72 even in the case where the maximumamount of current is supplied to the paths connected to the commonelectrodes 49 by simultaneous driving of all the piezoelectric elements41. That is, in the case where the maximum amount of current flowingfrom each piezoelectric element 41 to the common electrode 49 is I, thenumber of the piezoelectric elements 41 connected to the commonelectrode 49 is n, the allowable current density of the material of thesecond through electrodes 72 is i, the cross-sectional area of eachsecond through electrode 72 is A, and the number of the second throughelectrodes 72 is N, the number of the second through electrodes 72 andthe diameter of each of the second through electrodes 72 are determinedso as to satisfy a relationship “N>(I×n)/(I×A)”.

There will be explained selection of the number of the second throughelectrodes 72 by way of specific example. It is assumed that the maximumamount of current I flowing from one piezoelectric element 41 to thecommon electrode 49 is 10 mA (=1.0×10⁻² A), the allowable currentdensity i of copper (Cu) forming the second through electrodes 72 is0.5×10⁴ A/mm², and the number n of the piezoelectric elements 41 (thenumber of the nozzles 36) is 800. In this case, the number of therequired second through electrodes 72 changes as follows, depending uponthe diameter d of the through hole 74.

In the case where the diameter d is 40 μm, the cross-sectional area A is1.3×10⁻³ mm², and the number N is greater than 1.23. Two second throughelectrodes 72 are required at the least. In the case where the diameterd is 30 μm, the cross-sectional area A is 7. 1×10⁻⁴ mm², and the numberN is greater than 2.25. Three second through electrodes 72 are requiredat the least. In the case where the diameter d is 20 μm, thecross-sectional area A is 3.1×10⁻⁴ mm², and the number N is greater than5.1. Six second through electrodes 72 are required at the least.

It is noted that the above-described expression indicates the minimumnumber of required second through electrodes 72. Thus, in reality, thenumber of the second through electrodes 72 is preferably the numberobtained by adding one or more to the number N obtained according to theabove-described expression for the sake of reliability.

The driver IC 37 is pressed against and joined to the individualterminals 65 disposed on the top wall 53. To prevent deformation of thetop wall 53 due to a pressing force of the driver IC 37 during itsjoining, the individual terminals 65 are preferably provided on theright and left end portions of the top wall 53 which are coupled to therespective side walls 54 or on the central portion of the top wall 53which is coupled to the separated wall 55. In the present embodiment,the individual terminals 65 are disposed on the central portion of thetop wall 53.

In the present embodiment, the separated wall 55 has the first throughelectrodes 71 that conduct with the respective individual terminals 65disposed just above the respective first through electrodes 71. In thisconstruction, the first through electrodes 71 drawn out from the twopiezoelectric element rows 47 located on opposite sides of the separatedwall 55 are intensively disposed on the separated wall 55, resulting inreduced sizes of the piezoelectric actuator 24 and the protector 26 inthe right and left direction.

As illustrated in FIG. 5, the first through electrodes 71 and the secondthrough electrodes 72 are formed on the central portion of the separatedwall 55 in the right and left direction. With this construction, even inthe case where the pressing force acts on the separated wall 55 duringjoining of the driver IC 37, it is difficult for a bending force to acton the through electrodes 71, 72 disposed in the separated wall 55,thereby preventing breakage of the through electrodes 71, 72.

The FPC 27 is pressed against and joined to the input terminals 61disposed on the top wall 53. Like the individual terminals 65, the inputterminals 61 are preferably provided on portions of the top wall 53which are coupled to the side walls 54 or the separated wall 55 toprevent deformation of the top wall 53 due to the pressing force duringjoining of the FPC 27. In the present embodiment, the input terminals 61are formed on the right end portion of the top wall 53 which is coupledto the right side wall 54.

There will be next explained a process of producing the head unit 16with reference to FIGS. 9A-10I, mainly focusing on a process ofproducing the protector 26 and a process of joining the protector 26 tothe piezoelectric actuator 24. It is noted that the following steps A-Irespectively correspond to FIGS. 9A-10I.

There will be next explained the process of producing the protector 26with reference to FIGS. 9A-9F. In step A, recessed holes 81 that are toserve as the first through holes 73 are formed by etching in a siliconsingle crystal substrate 80 that is to serve as the protector 26. Instep B, a conductive layer 82 is formed on the substrate 80 by, e.g.,spattering from a side of the substrate 80 on which the holes 81 areformed. The conductive material forming the conductive layer 82 partlyenters the holes 81. In step C, the substrate 80 is ground from itsopposite sides to the two two-dot chain lines indicated in FIG. 9B toremove opposite end portions of each of the holes 81. As a result, thefirst through electrodes 71 filled with the conductive material areformed in the respective first through holes 73.

In step D, the insulating layers 75, 76 are respectively formed on thelower surface and the upper surface of the substrate 80 after thegrinding. The insulating layers 75, 76 are also etched to form the holes75 a, 76 a each smaller than a corresponding one of the first throughholes 73. In step E, the wires and the terminals such as the signalinput terminals 62, the individual terminals 65, and the signal wires68, are formed on the upper surface of the substrate 80 by plating with,e.g., gold (Au) or patterning of a thin layer of aluminum (Al). In stepF, a lower portion of the substrate 80 is etched to form recesses 83. Asa result, the production of the protector 26 including the top wall 53,the two side walls 54, and the separated wall 55 is finished.

There will be next explained, with reference to FIGS. 10G-10I, processesfrom the process of joining the protector 26 to a process of joining thedriver IC 37 and the FPC 27. In step G, the conductive adhesive 60 (ACFor ACP) is applied to the lower surface of the protector 26, and thenthe protector 26 is heated and pressed against the piezoelectricactuator 24 including the piezoelectric elements 41. As a result, theprotector 26 is mechanically joined to the piezoelectric actuator 24 ina state in which the driving contacts 57 and the first throughelectrodes 71 conduct with each other.

In step H, the first passage definer 21 is ground to reduce itsthickness to a particular thickness, and thereafter the first passagedefiner 21 is etched to form the pressure chambers 28. In step I, thedriver IC 37 is joined to the central portion of the top wall 53 of theprotector 26 with the conductive adhesive 64. The FPC 27 is thereafterjoined to the right end portion of the protector 26 with the conductiveadhesive 64. It is noted that the joining of the driver IC 37 and thejoining of the FPC 27 may be performed at the same time.

In the embodiment described above, the head unit 16 is one example of aliquid ejection apparatus. The front and rear direction in which thepiezoelectric elements 41 are arranged is one example of a firstdirection. The right and left direction parallel with a plane on whichthe piezoelectric elements 41 are arranged and orthogonal to the frontand rear direction is one example of a second direction. Thepiezoelectric actuator 24 is one example of an actuator. Each of thedriving contacts 57 is one example of a first contact. Each of theground contacts 58 is one example of a second contact. The top wall 53of the protector 26 is one example of a first wall. Each of the sidewalls 54 and the separated wall 55 is one example of a second wall. Eachof the individual terminals 65 formed on the top wall 53 is one exampleof a first connection terminal. Each of the first ground terminals 67 isone example of a second connection terminal. Each of the input terminals61 is one example of a third connection terminal. The insulating layer75 is one example of a first insulating layer. The insulating layer 76is one example of a second insulating layer. Each of the lowerelectrodes 42 of the respective piezoelectric elements 41 is one exampleof a first electrode. Each of the upper electrodes 44 of the respectivepiezoelectric elements 41 is one example of a second electrode. Thedriver IC 37 is one example of a drive circuit. The FPC 27 is oneexample of a wiring member.

While the embodiment has been described above, it is to be understoodthat the disclosure is not limited to the details of the illustratedembodiment, but may be embodied with various changes and modifications,which may occur to those skilled in the art, without departing from thespirit and scope of the disclosure. It is noted that the same referencenumerals as used in the above-described embodiment are used to designatethe corresponding elements of the modifications, and an explanation ofwhich is dispensed with.

In the case where the first through holes are formed in the protector byetching, each hole easily tapers down toward a deep side in a directionof travel of the etching. In a modification, as illustrated in aprotector 26A in FIG. 11, first through holes 73A are preferably formedby etching the protector 26A from an opposite side (an upper side) ofthe protector 26A from a side on which a piezoelectric actuator 24A islocated such that the diameter of each of the first through holes 73Adecreases with decrease in distance to the piezoelectric actuator 24A.

As is apparent from FIG. 11, when comparing the driving contacts 57located under the protector 26A and the individual terminal 65 locatedabove the protector 24A with each other, there is a larger space for theindividual terminal 65. Thus, the pitches of the individual terminals 65can be increased more easily than those of the driving contacts 57.Conversely speaking, since it is difficult to increase the pitches ofthe driving contacts 57, the diameter of each of first throughelectrodes 71A is preferably smaller at its lower portion than at itsupper portion to reliably prevent shorts at its lower end portion.

In another modification, one or both of the insulating layer 75 coveringthe lower end faces of the first through electrodes 71 and theinsulating layer 76 covering the upper end faces of the first throughelectrodes 71 in FIGS. 5-6B may be omitted. In FIG. 12, no insulatinglayer is formed on either of a lower surface and an upper surface of aprotector 26B. In particular, the insulating layer 75 may be omitted inthe case where the area of a lower end face of each of first throughelectrodes 71B is smaller than the area of a corresponding one of thedriving contacts 57. The insulating layer 76 may be omitted in the casewhere the area of an upper end face of each of a first throughelectrodes 71B is smaller than the area of a corresponding one of theindividual terminals 65.

In the above-described embodiment (see FIG. 3), the first groundterminals 67 connected to the common electrodes 49 and the second groundterminals 70 connected to the driver IC 37 are provided on the uppersurface of the top wall 53 of the protector 26 as the ground terminals.In yet another modification, a single type of ground terminals may beformed instead of the first ground terminals 67 and the second groundterminals 70.

In a head unit 16C illustrated in FIG. 13, for example, two groundterminals 67C are respectively disposed on opposite sides of theindividual terminals 65 in the front and rear direction. The groundterminals 67C are connected to the respective ground input terminals 63by respective ground wires 69C formed on the upper surface of the topwall 53 of the protector 26. The ground terminals 67C are connected tothe common electrodes by second through electrodes 72C formed in theprotector 26. The ground terminals 67C are also connected to a driver IC37C. In the construction illustrated in FIG. 13, the ground wires aresimplified, and wiring is easy when compared with the constructionillustrated in FIG. 3. In addition, the number of the terminals on thetop wall 53 is reduced, resulting in reduced size of the protector 26.

In the above-described embodiment, as illustrated in FIG. 5, the driverIC 37 is disposed on the central portion of the top wall 53 in the rightand left direction which is coupled to the separated wall 55, and theFPC 27 is joined to the end portion of the top wall 53 in the right andleft direction which is coupled to the side wall 54. In yet anothermodification, both of the driver IC 37 and the FPC 27 may be disposed ata portion of the top wall 53 which is coupled to one of the side walls54 or the separated wall 55.

For example, in a head unit 16D illustrated in FIGS. 14 and 15,individual terminals 65D and signal terminals 66D are disposed at a lefthalf portion of a coupled portion of the top wall 53 which is coupled tothe separated wall 55, and input terminals 61D are disposed at a righthalf portion of the coupled portion. The driver IC 37 is disposed on theleft half portion of the central portion of the top wall 53 andconnected to the individual terminals 65D and the signal terminals 66D.The FPC 27 is joined to the right half portion of the central portion ofthe top wall 53 and connected to the input terminals 61D. First throughelectrodes 71D connected to the respective individual terminals 65D aredisposed in a left half portion of the separated wall 55. That is, thedriver IC 37, the individual terminals 65D, the signal terminals 66D,and the first through electrodes 71D are disposed to the left of thecentral portion of the separated wall 55.

In this modification as described above, the individual terminals 65Dand the signal terminals 66D connected to the driver IC 37, and theinput terminals 61D connected to the FPC 27 are disposed at the centralportion of the top wall 53. This construction shortens the length ofeach of signal wires 68D that connect between the driver IC 37 (thesignal terminals 66D) and the input terminals 61D when compared with theconstruction in the above-described embodiment (FIG. 3).

The signal wires 68D are formed on the surface of the top wall 53 of theprotector 26 and exposed at least during the production of the protector26. Thus, increase in the length of each of the signal wires 68Dincreases a possibility of occurrence of a problem such as breakage ofthe signal wires 68D during the process of producing the protector 26.Also, in the case where the protector is extended, contracted, ordeformed due to changes in an external environment such as temperatureand humidity, the long wire may cause adverse effects such as conductionfailures, shorts, and increase or decrease in resistance of the wire. Inthe present modification, in contrast, the signal wires 68D are short,thereby eliminating these adverse effects.

In the above-described embodiment, as illustrated in FIG. 5, the driverIC 37 is disposed on the portion of the top wall 53 which is coupled tothe separated wall 55 in which the first through electrodes 71 areformed. In contrast, as in a head unit 16E illustrated in FIG. 16according to yet another modification, a chip-on-film (COF) 90 as awiring member on which a driver IC 87 is mounted is joined to theportion of the top wall 53 which is coupled to the separated wall 55.The driver IC 87 is electrically connected to the individual terminals65 to output drive signals to the piezoelectric elements 41. In theabove-described embodiment, since the driver IC 37 and the FPC 27 areindividually joined to the protector 26, two electrically connectingsteps are required. In the construction in FIG. 16, however, the COF 90only needs to be joined to the protector 26, making it possible toreduce the number of electrically connecting steps.

In the above-described embodiment, the protector 26 covers the twopiezoelectric element rows 47 and includes not only the top wall 53 andthe two side walls 54 but also the separated wall 55 located between thetwo piezoelectric element rows 47. In yet another modification in FIG.17, in contrast, a protector 26F covers only one piezoelectric elementrow 47. That is, the protector 26F includes only a top wall 53F and twoside walls 54Fa, 54Fb without including the separated wall. The firstthrough electrodes 71 are formed in the left side wall 54Fa of theprotector 26F. The driver IC 37 is disposed on a left end portion of thetop wall 53F which is coupled to the side wall 54Fa. The FPC 27 isjoined to a right end portion of the top wall 53F which is coupled tothe right side wall 54Fb.

In the construction as illustrated in FIG. 17, the distance between thetwo adjacent first through electrodes 71 may be increased as follows.For example, in FIG. 18, the driving contacts 57 are drawn out rightwardrespectively from the piezoelectric elements 41 in one of thepiezoelectric element rows 47. However, the driving contacts 57 are notarranged in a row in the front and rear direction but arranged in astaggered configuration so as to form two contact rows 56F. Inaccordance with this arrangement, the first through electrodes 71 arealso arranged in a staggered configuration so as to form two electroderows 77F. In this construction, a distance P2F between two of the firstthrough electrodes 71 which are adjacent to each other in the front andrear direction is greater than the distance P1F between correspondingtwo of the piezoelectric elements 41 in the front and rear direction.This construction prevents shorts between the two first throughelectrodes 71 adjacent to each other.

In FIG. 19, a plurality of driving contacts 57G drawn out rightward fromthe respective piezoelectric elements 41 in one of the piezoelectricelement rows 47 are arranged in a row. However, the driving contacts 57Gare disposed so as to spread radially as a whole. Thus, the pitches P2Gof the first through electrodes 71 corresponding to the respectivepiezoelectric elements 41 in the one piezoelectric element row 47 in thefront and rear direction are greater than the pitches P1G of thepiezoelectric elements 41 in the one piezoelectric element row 47 in thefront and rear direction. This construction prevents shorts between thetwo first through electrodes 71 adjacent to each other.

In the above-described embodiment, as illustrated in FIGS. 5-6B, thedriver IC 37 is disposed on the portion of the top wall 53 which iscoupled to the separated wall 55 in which the first through electrodes71 are formed. It is not essential that the driver IC 37 is disposedjust above the first through electrodes 71, and the driver IC 37 may bedisposed at a position spaced apart from the first through electrodes71. In this construction, the driver IC 37 and the individual terminals65 located just above the first through electrodes 71 are connected toeach other by respective wires formed on the top wall 53.

The arrangement of the driving contacts for the piezoelectric actuatoris not limited to that in the above-described embodiment. All thedriving contacts for the piezoelectric elements may be drawn out in thesame direction and arranged in a row at one end portion of thepiezoelectric actuator. Alternatively, the printer 1 may be configuredsuch that wires are drawn out from the two piezoelectric element rowstoward opposite sides in the scanning direction, and driving contactsare arranged in each of opposite end portions of the piezoelectricactuator in the scanning direction.

There will be explained, with reference to FIG. 20, arrangement ofthrough electrodes, terminals, wires, and other similar componentsformed in and on the protector in the construction in which the drivingcontacts are drawn out from the two piezoelectric element rows in theright and left direction. In a head unit 16H illustrated in FIG. 20, twoside walls 54H of a protector 26H are joined to right and left endportions of a piezoelectric actuator on which driving contacts aredisposed. A plurality of first through electrodes 71H and two secondthrough electrodes 72H are formed on each of the side walls 54H.Individual terminals 65H conductive with the respective first throughelectrodes 71H and two ground terminals 67H conductive with therespective two second through electrodes 72H are formed on each of aleft end portion and a right end portion of a top wall 53H which arecoupled to the respective side walls 54H.

A driver IC 37H is disposed on a central portion of the top wall 53H inthe right and left direction which is coupled to a separated wall 55H.The driver IC 37H is connected to the individual terminals 65H disposedon the left end portion and the right end portion of the top wall 53H,respectively by individual wires 68H and connected to the groundterminals 67H respectively by ground wires 69H.

In the construction in FIG. 20, two rows of the first through electrodes71H which correspond to the respective two piezoelectric element rowsare disposed on the right and left side walls 54H corresponding to therespective two rows. This construction increases the distance betweeneach two of the first through electrodes 71 which are adjacent to eachother in the front and rear direction when compared with theconstruction illustrated in FIG. 7 in the above-described embodiment. Itis noted that a wiring member (COF) on which the driver IC is mountedmay be joined to the separated wall 55H instead of the construction inFIG. 20 in which the driver IC 37H is disposed just above the separatedwall 55H.

The protector 26 is joined to the piezoelectric actuator 24 with theconductive adhesive 60 in the above-described embodiment but may bejoined to the piezoelectric actuator 24 with non-conductive adhesive(NCF or NCP).

The ink-jet head 4 in the above-described embodiment is a serial headconfigured to eject the ink while moving in the widthwise direction ofthe recording sheet 100. However, the present disclosure may be appliedto a line head having nozzles arranged in the widthwise direction of thesheet.

While the present disclosure is applied to the ink-jet head configuredto eject the ink onto the recording sheet to record an image in theabove-described embodiment, the present disclosure may be applied toactuator devices used for purposes other than liquid ejection. Also, theactuator is not limited to the piezoelectric actuator including aplurality of piezoelectric elements. For example, the actuator may be anactuator including a heater as a drive element which causes driving byutilizing a heat generated when a current passes through the heater.

What is claimed is:
 1. An actuator device, comprising: an actuator comprising a plurality of piezoelectric elements arranged in a first direction and a plurality of first contacts respectively drawn from the plurality of piezoelectric elements and arranged in the first direction; a protector configured to cover the protector; a plurality of first connection terminals disposed on a surface of the protector, which surface is located on an opposite side of the protector from the actuator; and a plurality of first through electrodes respectively provided in a plurality of first through holes formed in the protector, the plurality of first through electrodes being configured to respectively bring the plurality of first contacts and the plurality of first connection terminals into conduction with each other, wherein a distance between two of the plurality of first through electrodes which respectively correspond to particular two of the plurality of piezoelectric elements, which are nearest to each other in the first direction among the plurality of piezoelectric elements, is greater than a distance in the first direction between the particular two of the plurality of piezoelectric elements, wherein each of the plurality of piezoelectric elements comprises a piezoelectric layer, a first electrode, and a second electrode, and the piezoelectric layer is interposed between the first electrode and the second electrode in a thickness direction of the piezoelectric layer, wherein a plurality of the first electrodes of the plurality of piezoelectric elements are separated from each other, and a plurality of the second electrodes of the plurality of piezoelectric elements conduct with each other so as to form a common electrode, wherein each of the plurality of first contacts is connected to a corresponding one of the plurality of the first electrodes of the plurality of piezoelectric elements, wherein the actuator comprises at least one second contact connected to the common electrode, wherein the actuator device further comprises: at least one second connection terminal disposed on the surface of the protector, which surface is located on the opposite side of the protector from the actuator; and at least one second through electrode provided in at least one second through hole formed in the protector, the at least one second through electrode being configured to bring the at least one second contact and the at least one second connection terminal into conduction with each other, and wherein a diameter of each of the plurality of first through holes formed in the protector is equal to a diameter of each of the at least one second through hole formed in the protector.
 2. The actuator device according to claim 1, wherein, in a case where a thickness of the protector is defined as t, a diameter of each of the plurality of first through holes is equal to or greater than t/10.
 3. The actuator device according to claim 2, wherein the diameter of each of the plurality of first through holes is equal to or greater than 40 μm.
 4. The actuator device according to claim 1, wherein the actuator comprises a plurality of second contacts as the at least one second contact, wherein a plurality of second connection terminals as the at least one second connection terminal are provided on the protector, and wherein a plurality of second through electrodes as the at least one second through electrode are provided on the protector, and the plurality of second through electrodes are respectively configured to bring the plurality of second contacts and the plurality of second connection terminals into conduction with each other.
 5. The actuator device according to claim 1, wherein the plurality of piezoelectric elements form two piezoelectric element rows arranged side by side in a second direction that is parallel with a plane on which the plurality of piezoelectric elements are arranged and that is orthogonal to the first direction, wherein a plurality of piezoelectric elements in each of the two piezoelectric element rows are arranged in the first direction, wherein the plurality of first contacts are drawn outward in the second direction from the plurality of piezoelectric elements arranged in the two piezoelectric element rows, and wherein the plurality of first through electrodes conductive with the plurality of first contacts are provided outside a portion of the protector which is located between the two piezoelectric elements rows in the second direction.
 6. The actuator device according to claim 1, wherein the protector and the actuator are joined to each other with conductive adhesive containing a conductive particle.
 7. The actuator device according to claim 6, wherein a thickness of the conductive adhesive is less than a thickness of each of the plurality of piezoelectric elements in the thickness direction.
 8. The actuator device according to claim 1, wherein the plurality of first contacts are respectively disposed right below the plurality of the first through holes.
 10. The actuator device according to claim 1, wherein the plurality of first through electrodes form a first electrode row and a second electrode row arranged side by side in a second direction that is parallel with a plane on which the plurality of piezoelectric elements are arranged and that is orthogonal to the first direction, wherein a plurality of first through electrodes in the first electrode row are arranged in the first direction, and a plurality of first through electrodes in the second electrode row are arranged in the first direction, wherein each of the plurality of first through electrodes in the first electrode row is different, in position in the first direction, from a corresponding one of the plurality of first through electrodes in the second electrode row, and wherein a distance between a center of each of the plurality of first through electrodes in the first electrode row and a center of a corresponding one of the plurality of first through electrodes in the second electrode row in a direction of a straight line connecting between the center of said each of the plurality of first through electrodes in the first electrode row and the center of a corresponding one of the plurality of first through electrodes in the second electrode row is greater than a distance in the first direction between said each of the plurality of first through electrodes in the first electrode row and the corresponding one of the plurality of first through electrodes in the second electrode row.
 11. The actuator device according to claim 1, further comprising a first insulating layer provided on a surface of the protector, which surface is joined to the actuator, wherein the first insulating layer covers an actuator-side end face of each of the plurality of first through electrodes, and wherein the first insulating layer comprises a hole smaller than the actuator-side end face of each of the plurality of first through electrodes.
 12. The actuator device according to claim 11, wherein an area of the actuator-side end face of each of the plurality of first through electrodes is greater than an area of each of the plurality of first contacts.
 13. The actuator device according to claim 1, further comprising a second insulating layer provided on the surface of the protector, which surface is located on the opposite side of the protector from the actuator, wherein the second insulating layer covers an opposite-side end face of each of the plurality of first through electrodes, which end face is located on an opposite side of said each of the plurality of first through electrodes from the actuator, and wherein the second insulating layer comprises a hole smaller than the opposite-side end face of each of the plurality of first through electrodes.
 14. The actuator device according to claim 1, wherein each of the plurality of first through holes formed in the protector tapers down toward the actuator. 